[OwnCloud] DAVdroid just sync contacts without group membership

DAVdroid just sync contacts without a group membership. The problem was identified with OwnCloud 7.0.2. So I used the chance to update to OwnCloud 8.2.0 . The problem is still there. I don't synchronize my OC-Account with any other device just by Sony Z3 compact.

Some ideas where the problem could be?

DAVdroid 0.9.1
Sony Xperia Z3 compact (Android 5.1.1)

Theoretically DAVdroid supports groups via the vCard3 "CATEGORIES" field and Owncloud uses this kind of group management, or at least I know that it used it in the past... I've no idea where the problem may be in this case, since I don't know OC so well...

I have same problem with android 5.1.1 (Sony Z1 compact) and Owncloud (8.2.2) and davdroid 1.0.8 (last version available in f-droid)

Owncloud send all contact (format seem ok), davdroid received all contact and in log file davdroid indicated that all contact is added. But all contact with 'CATEGORIES:' field are not available in phone.
Owncloud group are not created in phone, but i can create group in phone and add contacts, in that case, group appear in owncloud. But if, i remove account and create same account, there is same problem, group are not re-created and contacts in that group are not available in phone.

I can't find other contact editor on f-droid and i don't have Play (google) account.
But i have find contact exporter, and in exported file, i see missing contact, but without 'CATEGORIES' field (perhaps bug in export application)